The invention relates to a method of producing a cooling channel piston for an internal combustion engine.
It is fundamentally known to produce blanks for pistons by casting or forging which possess a cooling channel after final machining. Combinations of both the aforementioned processes are also possible. Forging lends itself to this production method since a piston produced by forging has superior strength properties compared to a piston produced by casting. In the case of piston blanks produced by forging, a complicated process is required to introduce a cooling channel into this piston blank in the ring belt region. In contrast to cast piston blanks, the lost core method cannot be employed with forged pistons. Consequently, the introduction of the cooling channel using appropriate steps causes a recurring problem. A known method is to introduce a radially circumferential recess by metal-cutting machining and to close said recess by suitable means. In so doing, close attention must be paid to the dimensional accuracy of the recess and of the means to close this recess. The result is an additional cost-intensive procedure. The elements involved are correspondingly complicated to manufacture because of the required dimensional accuracy.
A generic method is known from DE 35 02 248 C1 for producing a single-piece piston for a combustion engine by forging. In this process, a piston blank is produced having a pre-form collar, when this collar is turned down at an angle in the upper area of the piston crown by forming over, a piston crown shoulder is created which together with an area of a piston crown pre-form creates a heat-restricting annular gap. Because the collar is formed over in the upper areas of the piston crown, rounded edges are created initially which require reworking of the lateral and top surfaces of the piston blank. A substantial disadvantage additionally results from forming, which weakens the piston crown so that a piston produced in this way is no longer adequate to meet the demands of modern combustion engines with respect to the increased ignition pressures and combustion temperatures required to meet exhaust emissions requirements.
A method of producing a cooling channel piston is known from DE 103 09 016 in which at least one circumferential flange is formed on a forged piston blank specifically in the area of a top land. A recess is introduced behind the at least one flange and subsequently the at least one flange is formed over in such a way that the recess is closed by the at least one flange to form the cooling channel. This process offers one design possibility and a method of producing a cooling channel. The object of the invention is to propose a further method, in addition to the already known method of producing cooling channel pistons, which can be applied to all types of pistons.